1. Field of the Invention
The present invention relates to a display control system suited for use in a laptop type personal computer that, for example, incorporates a plurality of types of display drive circuits.
2. Description of the Related Art
Recently, a variety of portable laptop type personal computers operable by an internal battery have been developed. In order to expand applicable fields of these laptop type personal computers having improved performance characteristics, there is a positive demand to realize a display drive function capable of driving plural kinds of display devices. To satisfy this demand, it is essential for the laptop type personal computer to provide proper display control circuits for the display devices of the computer. More specifically, when driving a flat-panel display such as a plasma display (hereinafter referred to as PDP), a liquid crystal display (hereinafter referred to as LCD), and a CRT display, for example, the PDP and the CRT display can be controlled by common timing signals. On the other hand, the PDP and the LCD, both a flat-type display, have different display timing signals. For this reason, the PDP and the LCD must respectively have an independent display control circuits including display memories dedicated for the respective display units.
However, when the display control circuits for the above display units are incorporated in the computer, the LCD display control circuit not used is set in an operative mode even if the PDP is being driven. For this reason, wasteful power dissipation is caused by the LCD display control circuit. Particularly, when the computer is driven by the internal battery, the battery operation time is shortened. Furthermore, the flat panel display unit such as the PDP and the back-lit LCD requires a high voltage for illuminating the panel (a discharge voltage for the PDP and an electroluminescence (EL) drive voltage). For this reason, the drive power supply including the above high voltage circuit dissipates relatively large amount of power.